A Morphometric Study of Species Boundaries of the Wild Potato Solanum Series Piurana (Solanaceae) and Putatively Related Species from Seven Other Series in Solanum Sect. Petota

There are about 190 wild potato (Solanum L. section Petota Dumort.) species distributed from the southwestern United States to central Argentina and adjacent Chile and Uruguay. The morphological similarity of many of its constituent species has led to widely conflicting taxonomic treatments. Solanum series Piurana Hawkes is one of 21 series recognized in section Petota in the latest comprehensive taxonomic treatment by Hawkes in 1990. They are distributed from southern Colombia, south through Ecuador to central Peru. The limits of the series and validity of its constituent species are unresolved. We provide the first comprehensive morphological phenetic study of the series, to include putatively related species in ser. Conicibaccata, Cuneoalata, Ingifolia, Megistacroloba, Simplicissima, Tuberosa, and Yungasensa, through an examination 188 living germplasm accessions of 33 species, planted in replicated plots in a field station in Andean Peru. Only four morphologically well-defined groups were supported. Continuing work is exploring molecular support for these species in these eight series. Keywords—morphometrics, Peru, potatoes, Solanaceae, Solanum section Petota, Solanum series Piurana. The genus Solanum L. is one of the most important genera of the Solanaceae. There are about 190 wild tuber-bearing species (Solanum sect. Petota Dumort.), distributed from the southwestern United States to central Argentina and adjacent Chile and Uruguay. The morphological similarity of many species in the section has led to widely conflicting taxonomic treatments (Spooner and Salas 2006). Solanum series Piurana Hawkes is one of 21 series recognized in section Petota in the latest comprehensive taxonomic treatment by Hawkes (1990). They are distributed from southern Colombia, south through Ecuador to central Peru. The limits of the series and its constituent species are unresolved and controversial. The most distinctive features of ser. Piurana, used by all major taxonomists of section Petota (Correll 1962; Hawkes 1990; Ochoa 1999) are the globose to ovoid fruits and the coriaceous glossy leaves. However, these traits vary so much across the different series that it is difficult to decide what to include in ser. Piurana. All the above authors have expressed doubts about the limits of ser. Piurana; as stated by Correll (1962: pg.139), “This series, probably more than any others, may be considered a catchall. Paradoxically, its component species are held together not so much by their similarity as by their differences.” Different taxonomic treatments illustrate the disagreements regarding the limits of the series. Correll (1962) recognized 15 species, Hawkes (1990) 15, and Ochoa (1999) 13; however, they recognize only six species in common: S. acroglossum [see Table 1 for authors of species names], S. cantense, S. cyanophyllum Corr. (= S. andreanum Baker [Spooner et al. 1993]), S. hypacrarthrum, S. piurae, and S. solisii (Table 1). Plastid DNA restriction site and morphological data (Castillo and Spooner 1997; Spooner and Castillo 1997) suggested that Solanum ser. Piurana as traditionally circumscribed was paraphyletic. Salas et al. (2001) pointed out that all the species placed by Hawkes (1990) and Ochoa (1999) in ser. Piurana possess moniliform tubers (like beads along the stolons, unlike the more typical arrangement of single tubers placed at stolon ends). Spooner and Salas (2006) suggested that the only two distinctive features of ser. Piurana might be the coriaceous and glossy leaves (Correll 1962; Hawkes 1990; Ochoa 1999), and the moniliform tubers. Based on the plastid DNA restriction site data, survey of leaf and tuber morphology by Ochoa (1999), and knowledge of these traits in the field and greenhouse, Spooner and Salas (2006) provided hypotheses of a redefined and enlarged monophyletic ser. Piurana to include all members of series Piurana (all 15 species) as recognized by Hawkes (1990) and selected species in ser. Conicibaccata Bitter (four of 40), Cuneoalata Hawkes (all three), Ingifolia Ochoa (two of two), Megistacroloba Cárd. and Hawkes (one of 11), Olmosiana Ochoa (one of one), Simplicissima Ochoa (one of one), Tuberosa (Rydb.) Hawkes (15 of 94), and Yungasensa Correll (one of nine). In total, these 43 species represent 19% of the total 225 species recognized by Hawkes. The primary goal of this study is to analyze the morphological support for the validity of species in this expanded concept of a putatively monophyletic ser. Piurana as suggested by Spooner and Salas (2006). The data will be useful to redefine the number of species in sect. Petota, for comparison to molecular results, and for a taxonomic monograph of these species that is currently in progress. MATERIALS AND METHODS Plant Material—A total of 188 accessions from 33 of the 43 different species of ser. Piurana and putatively related wild potato species (see above) from other series were selected for the morphological analysis (Appendix 1). We did not collect data for the 10 remaining species because they were not available as germplasm (four species) or did not grow well in the greenhouse (six species). These accessions include representatives of all of the nine series listed above except for ser. Olmosiana, which grew poorly in our study. Figures 1–3 illustrate the range of variation in tubers, leaves, flowers, and fruits within these eight series. Plants were grown from seeds provided by the US Potato Genebank in Sturgeon Bay, Wisconsin (http://www.ars-grin.gov/nr6/) and the International Potato Center (http://www.cipotato.org/). More than one accession per taxon was analyzed (when available); not all species had the same number of accessions due to their rarity and restricted geographical distribution. Higher numbers of accessions were considered for some species, such as S. andreanum and S. chomatophilum due to their wide geographic distribution and/or great morphological variation. Herbarium vouchers were deposited at the International Potato Center herbarium (CIP) in Lima, Peru. The evaluated accessions were mapped with ArcGIS (ESRIInc., 2005), and grouped by generalized geographic areas (Fig. 4; Appendix 1). Morphological Evaluation—The accessions were grown in greenSystematic Botany (2008), 33(3): pp. 566–578 © Copyright 2008 by the American Society of Plant Taxonomists